Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$215.43	11.600%	$240.4199	$240.42	$240.40	$240.40
Purchase #2	$237.77	10.412%	$262.5266	$262.53	$262.55	$262.50
Purchase #3	$62.65	8.450%	$67.9439	$67.94	$67.95	$67.90
Purchase #4	$63.73	3.165%	$65.7471	$65.75	$65.75	$65.70
Purchase #5	$20.50	4.228%	$21.3667	$21.37	$21.35	$21.40
Purchase #6	$38.47	7.759%	$41.4549	$41.45	$41.45	$41.50
Purchase #7	$181.66	3.826%	$188.6103	$188.61	$188.60	$188.60
7 purchase totals =	$820.21		$888.0694	$888.07	$888.05	$888.00